A helicopter is ascending vertically with a speed of 8m/s. At a height of 120m above the earth, a stone is dropped from a window. How much time does it take for the stone to reach the ground.

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answer is 5.83S.

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Detailed Solution

Initial speed u=8 m/sHeight h=120 mFrom equation of height of tower h=12gt2−ut⇒120=12×9.8×t2−8t⇒4.9t2−8t−120=0t=8±64+4×4.9×1202×4.9t=8±49.159.8t=5.83s (only positive value)

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